Renal tubular reabsorption of trace alkaline earths compared with calcium

¹ Department of Pharmacology and Experimental Therapeutics and Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland

Simultaneous clearances of inulin, calcium, and either Be⁷, Ba¹⁴⁰, or Ra²²⁶, given by constant infusion, were measured in salt-depleted dogs or dogs undergoing mild saline, mannitol, or sulfate diuresis. Urine-to-plasma ratios of all three cations less than 0.5 were noted, suggesting that all can be actively reabsorbed. Clearances of barium and radium were correlated with calcium clearance, but the clearance of beryllium was unpredictable. Protein binding of beryllium was shown to be of the same order of magnitude as other alkaline earths when errors due to adsorption of Be⁷ onto containers were minimized. Protein binding of barium averaged 54%. The excreted-to-filtered ratio for barium was a constant power (.54) of the ratio for calcium. The data do not exclude the possibility that these cations are reabsorbed by a common transport mechanism with calcium.

Key Words: beryllium • barium • radium • renal tubule • protein binding

Submitted on October 21, 1964